Fixtures, reusable state for writing clean tests and more.

Fixtures defines a Python contract for reusable state / support logic,
primarily for unit testing. Helper and adaption logic is included to make
it easy to write your own fixtures using the fixtures contract. Glue code
is provided that makes using fixtures that meet the Fixtures contract in
unittest compatible test cases easy and straight forward.

Note:
There is a cyclic dependency between testtools package and fixtures package.
Since these are python libraries, one has to just install both of them.
